But if some people had had their way, it wouldn't be there. In order to get enough velocity to make it to Jupiter, it was necessary for Cassini to make several passes near planets in the inner Solar system, including one past the Earth.

In the outer solar system there isn't enough light from the sun to power a satellite with photocells. So all the satellites which go to the outer system carry nuclear power plants -- in particular, several pounds of refined plutonium, which is constantly warm. They then use that heat to generate electricity which powers the craft. This was true of both Voyager craft, of Galileo (which is at Jupiter now) and of Cassini, on its way to Saturn.

Just before the gravity assist at the Earth, some luddites tried to get a court order to force NASA to change the course of Cassini so that it wouldn't come close to the Earth. Doing so would have destroyed its orbit and aborted the mission. They were afraid that the craft might actually hit the earth, and that its plutonium would be released into the atmosphere -- and apparently that millions of people would have died, or something like that. Given that hundreds of pounds of plutonium are already in the atmosphere from all the atmospheric nuclear tests in the 1950's, it's hard to see how the 6 or 7 pounds in Cassini would make much difference. But the whole issue was moot, because Cassini wasn't going to hit the earth. NASA had the orbit under control.

Fortunately, NASA was able to convince the appropriate federal judge to dismiss the suit before the encounter, and were permitted to make the earth flyby on schedule. It went flawlessly, as expected.

But had certain hyper-suspicious Luddites had their way, this mission would have failed before it began. I get really tired of people who get terrified of anything which has the word "radiation" attached to it.

Here is a picture of one of the power generation units. Notice that they talk around the issue. The picture refers to a "general purpose heat source" and never mentions that it is plutonium.

This page talks about the orbit they used. It required two passes by Venus and one by the Earth to pick up enough velocity to leave the inner solar system.posted by Steven Den Beste at 11:12 PM on December 30, 2000

Given that I believe that the RTGs used in Cassini are safe, I would hardly characterize concerns about nuclear contamination as Luddism. Radiation is safe, if handled correctly, but incorrectly, it can be very, very unsafe, and the invisibility of its reach and the long, indirect association with effects easily creep many people out, including me.posted by dhartung at 11:37 PM on December 30, 2000

Oh, my. Luddite? Well. . .

Fact: Cassini's launch, on the ol' Titan IV rocket, represented about a one in ten chance of inadvertant reentry, which NASA admitted would expose 5-6 billion of the world's population to plutonium.

Fact: although not yet tested in space flight, solar panels have been invented that would make missions to the outer solar system possible without RTGs. Given the risks, we should have waited with Cassini (Saturn is not going away anytime soon).

I don't know the facts well enough to comment, but aren't all major technological developments protested in some way or another? Benign or otherwise?

I'm reminded of a (can't remember the name) group that tried to stop a Particle Accelerator because they believe ('hypothesized") that it would generate a black hole that would consume the Earth. (ok, technically I understand it wasn't a "black hole", but rather a cosmic string of sorts, but same idea.) Absurd stuff.

I don't believe that NASA is THAT stupid when it comes to endangering lives....unless the whole project is a giant government/alien/illuminati/midget conspiracy...

Plutonium is far from the most toxic substance on earth. I'm really getting tired of hearing that particular exaggeration. And the idea that one atom could be fatal is preposterous. The chance of one atom killing someone is not zero, but it is vanishingly small.

Ounce for Ounce, mutated anthrax is probably about a million times as dangerous. One test tube of the stuff really is capable of starting a plague which could eradicate all mammalian life on earth.

Or compare it to Arsine gas, which is fatal in unbelievably small doses. But Arsine is used industrially; it's a vital component in the manufacture of integrated circuits. (So is phosphine, which is equally dangerous.)

There are many substances which are used routinely which are exceedingly dangerous. It doesn't make sense to single this one out for hysterical reaction while ignoring all the others.

What you do is treat them with respect, but otherwise go about your business.

It is also a fact that A-bomb explosions are not very efficient, and most of the U-235 or Plutonium involved isn't fissioned. Instead, it's simply vaporized and becomes part of the dustcloud formed. In the fifties, the US and Russia between them exploded many dozens of such bombs in the atmosphere each of which contained far more radioactives than Cassini contains, and almost all of those atoms were simply distributed into the air. If plutonium were as dangerous as you say, we'd all be dead by now; Earth's weather has long since spread those atoms everywhere. You've certainly been exposed to far more than "one atom" of plutonium (probably several orders of magnitude more than that), but you're alive and kicking.

But the real point is that the danger of Cassini hitting the earth was vanishingly small. That lawsuit was fundamentally really stupid, a knee-jerk reaction to "radioactivity". More to the point, it was inconsistent because it overreacted to this danger while ignoring all the others which are at least as deadly.

It was a nutty physicist who suggested that, mkn, and the as far as I know any protests were largely fanned up by sensationalist media figures.posted by snarkout at 9:50 AM on December 31, 2000

I'm getting really tired of hearing vitriol spewed just because someone raises concerns about the safety of scientific projects. Is NASA taking safety precautions? Of course. But does NASA have a perfect track record? Of course not.

We should not let the most hyperbolic voices shut down all scientific advancement, but neither should we blindly accept all experimentation done in the name of science. If we stop questioning the propriety of such experiments, we're all dead. Science is not by nature altruistic. It just exists, and must be subject to the same scrutiny as any other human endeavor.posted by ChrisTN at 10:37 AM on December 31, 2000

I thought the concerns over the spacecraft crashing into the earth unlikely, until I read that the last Mars probe missed its orbit because NASA failed to convert metric units into English units.posted by Poop(*)Head at 1:04 PM on December 31, 2000

ceiriog: Wasn't Mir supposed to be decomisioned ages before the accidents?posted by davidgentle at 8:34 PM on December 31, 2000

It's often forgotten that Mir was to be replaced by Mir 2 long ago, but its lifetime was extended in part to support the Shuttle-Mir program, aka International Space Station Phase I. In other words, if it weren't for the US Congress cancelling the space station, and the White House desperately trying to save it by making it an international project, Mir indeed would have been decommissioned and the resources that were used to keep it running would have been devoted to replacing it instead. Still, I would have written "expected to be decommissioned".

Space activities are not without risk. Still, I believe they're worth doing, as long as we're honest to ourselves.posted by dhartung at 1:23 AM on January 1, 2001

The use of the term Luddite may be a little strong, Steven.

Nevertheless, I'm glad its up there. Here's a neat picture taken a few weeks ago from its fly past. It shows Io casting a shadow on Jupiter's atmosphere.posted by lagado at 2:51 AM on January 1, 2001

Mir has vastly exceeded its operational expectancies. It was launched in 1986, with a planned lifespan of only five years.posted by Aaaugh! at 9:29 AM on January 1, 2001

Luddites?! At least they knew what they were talking about, Steven.

You may have some contempt for those "Luddites", but that's nothing compared to their contempt for the people who decided it was okay to put 72 pounds (not the "six or seven" pounds you erroneously mentioned) of the deadliest substance known to man atop a rocket that has been known to blow up on occasion.

Pardon me if I think that wasn't the brightest move NASA ever made. I don't think that makes me a "Luddite".

True, the post-launch Earth flyby wasn't as dangerous as the launch itself, but it was still worrisome. NASA changed the figures for just how close the probe was supposed to come to the Earth several times. That, combined with recent crash of a Mars probe, didn't exactly inspire people's confidence. I think those "Luddites" were right to be concerned.posted by Potsy at 3:28 PM on January 1, 2001

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